p53 and PCNA Expression in Keratocystic Odontogenic Tumors Compared with Selected Odontogenic Cysts.

p53 and PCNA expression in keratocystic odontogenic tumors compared with selected odontogenic cysts Summary: The aim of this study was to evaluate p53 and PCNA expression in different odontogenic lesions regarding their different clinical behaviors. Slices prepared from 94 paraffin-embedded tissue blocks (25 radicular cysts (RC), 23 dentigerous cysts (DC), 23 keratocystic odontogenic tumors (KCOT) and 23 calcifying cystic odontogenic tumors (CCOT)) were stained with p53 and PCNA antibodies using immunohistochemistry procedure. The highest level of p53 expression was in the basal layer of RC, and the highest level of PCNA expression was in the suprabasal layer of KCOT. The differences of p53 expression in basal and suprabasal layers as well as PCNA expression in the suprabasal layer were significant but there was no significant difference in PCNA expression in the basal layer of these lesions. The expression of p53 in the basal layer of RC was higher than in other cysts. This may be due to intensive inflammatory infiltration. Also, the high level of PCNA expression in the suprabasal layer of KCOT may justify its neoplastic nature and tendency to recurrence. KCOT and calcifying cystic odontogenic tumors did not show similar expression of studied biomarkers.


Materials and Methods
After the approval of the Institutional Ethics

Results
The percentage of p53 and PCNA stained cells in basal and suprabasal layers of radicular cyst, dentigerous cyst, KCOT and calcifying cystic odontogenic tumor (CCOT) are shown in Table 1.      cyst, dentigerous cyst and KCOT was higher than in the suprabasal layer (P=0.007, 0.024 and 0. 025, respectively), but there was no significant difference in CCOT (P=1.000).
In radicular cyst, PCNA expression in the basal layer was higher than in the suprabasal layer (P=0.003), but there was no significant difference in other cysts (KCOT, CCOT and dentigerous cyst, P=0.188, P=0.705 and P= 0.083, respectively). Therefore, the highest level of p53 and PCNA expression was found in the basal layer of radicular cyst and the suprabasal layer of KCOT, respectively.

Discussion
We studied the expression of p53 and PCNA in some odontogenic cysts. p53 expression was higher in the basal layer of radicular cyst, followed by KCOT. PCNA expression was higher in the suprabasal layer of KCOT, followed by radicular cyst. The relationship between p53 expression and cell proliferation was showen in de Oliveira et al.'s study. They concluded that p53 expression was seen in proliferating cells, but it accumulated due to several factors such as cellular stress. Also, they showed that in radicular and dentigerous cysts, the expression of p53 and PCNA is a response to cellular stress resulting from inflammation, even in the cases of developmental cyst such as dentigerous cyst (11).
Studies showed that growth factors and cytokines (Interleukin 1, Interleukin 6 and tumor necrosis factor) are released in inflammatory processes. Inflammation may cause cell proliferation and inflammatory cytokines may produce cellular stress (18).
In dentigerous cyst, the inflammatory stimulus may be the result of the eruption process that caused cellular proliferation which might be present for a short time (11). This could explain the lower expression of p53 and PCNA in dentigerous cyst. It was not proven that inflammatory stimuli could cause dentigerous cyst, but usually in the connective tissue of cyst, there was an inflammatory infiltration that might have caused epithelial cells proliferation. Kaplan and Hirschberg studied the areas with and without inflammation in KCOT and did not find a significant difference in their proliferation rate. They concluded that inflammation in KCOT did not have any effect on its proliferative potential (20). Also, in the present study all of KCOTs were non-inflamed.
Gallana-Alvarez and Wagner showed that the neoplastic cells in calcifying odontogenic cyst may have an increasing proliferative potential.
Calcifying odontogenic cyst is considered as a tumoral lesion and the presence of mutant proteins should be taken into consideration. P53 expression may be related to the proliferation rate in this lesion (21)(22).
However, in the present study, there was no high expression of p53 and PCNA in CCOT in comparison to other cysts. This differs from the study of de Oliveira who found a high level of p53 and PCNA in calcifying odontogenic cysts (11).
In our study, a significant difference between the percentages of stained cells was found for both